Continuous heat treating apparatus for metal strips



Feb. 28, 1967 HIROSH' HAG'WARA 3,307,015

CONTINUOUS HEAT TREATING APPARATUS FOR METAL STRIPS Filed June 10, 1964 2 Sheets-Sheet l FiG.I

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BY W W F 3, 1967 HIROSHI HAGIWARA 3,307,015

CONTINUOUS HEAT TREATING APPARATUS FOR METAL STRIPS Filed June 10, 1964 2 Sheets-Sheet 2 F" a' G1 4 LMJ ' I3 I EIZQDETECTOR 40 EFAMPLIFIER 4 so Q fiQo 1M IW 1N VEN TOR.

United States Patent $307,015 CONTINUOUS HEAT TREATING APPARATUS FOR METAL STRIPS Hiroshi Hagiwara, Takaoka-shi, Japan, assignor to San- Etsu 'Kinzoku Kogyo Kabushiki 'Kaisha, Takooka-shi, Japan, a joint-stock company of Japan.

Filed June 10, 1964, Ser. No. 373,948 Claims priority, application Japan, June 17, 1963, 38/ 32,019 7 Claims. .(Cl. 219-155) This invention relates to a continuous heat treating apparatus for metal strips and has as its general object the provision of a novel method of, and an apparatus for quickly heating and cooling continuously moving metal strips.

This invention may be best understood by referring to the following description taken in conjunction with the accompanying drawings in which like parts are designated by like reference characters, and in which:

FIGS. 1 and 2 are schematic representations indicating two conventional methods of heat treating strip metals;

FIG. 3 is a simplified perspective view of a set of concave pressure shoes and current carrying rolls, both these components being herein described also as rolls because of their similarity to conventional rollers or rolls employed in this invention;

FIG. 4 is a schematic diagram showing one embodiment of the apparatus according to this invention;

FIG. 5 is a front view of a modified set of rolls of the invention; and

FIG. 6 is a side view of a still further modification of the roll set of the invention.

There are two known methods of heat treating metal strips, namely, the batch process wherein metal strips are heated and cooled in the form of coils, and the so-called continuous process wherein a metal strip 1 unreeled from a supply reel and is continuously passed successively through a heating furnace A and a cooling tank B is finally wound upon a take-up reel as schematically shown in FIG. 1. To provide uniform heat treatment, the continuous process is more advantageous because by the batch process, as the kinds of temperature rise are different between the peripheral portion and the interior portion of the coil, the coil must be heat treated for a long period of time in order to effect uniform heat treatment.

As a result of recent research it was found that, when subjected to quick heating and quick cooling operations, metal strips of copper, brass or aluminum, for example, will not only have decreased resistance to buckling but also have fine crystalline structure thereby producing materials suitable for deep drawing operations. In order to effect such a rapid heating, it is obvious that a continuous process should be employed.

Gas, oil, electric power and the like are ordinarily used as the heat source of quick heating in the continuous process to heat metal strips from the outside, but I have investigated a method of heating the metal strip by directly passing electric current through the strip to elevate its temperature by the heat due to ohmic loss therein.

FIG. 2 shows the principle of this heating method wherein a voltage is app-lied across a pair of conductive rolls B and C around which a metal strip 1 is passed in the direction indicated by arrows to be heated continuously by the current flowing therethroug In the practice of this method in commercial production, the most difficult requirements'are intimate contact between the metal strip and the current carrying rolls despite the presence of some irregularities or buckli'ngs in the stripand the prevention of electric sparks at the contact points between the current carrying rolls 3 and C and the metal strip 1.

3,307,015 Patented Feb. 28, 1967 To fulfill these requirements in accordance with this invention, a press r0ll 3 made of a suitable elastic material such as rubber is employed to be urged against a current carrying roll 2 so as to make contact over a surface area indicated by a, b, c and a in FIG. 3. This ensures that the metal strip 1 being heat treated is in intimate contact with the current carrying roll 2 over a constant area while it is passed through rolls 2 and 3. Thus, by pressing the metal strip 1 with substantial force against the current carrying roll 2 by means of the press roll 3 made of elastic material, the strip can be caused to engage firmly the periphery of the current carrying roll 2 over a certain area, whereby sufiicient contact necessary for conduction of electric current is provided regardless of the presence of some irregularities or bucklin-gs in the metal strip 1.

In order to prevent excessive temperature rise of the press roll 3 as well as undesirable sparking thereof, it is preferable to immerse both rolls 2 and 3 in water. In the embodiment shown in FIG. 4, auxiliary rolls 4 and 4a are provided to bias the metal strip 1 away from the current carrying rolls 2 and 2a and toward the press rolls 3 and 3a for the purpose of preventing electric sparks from occurring due to unstable contact immediately before and after the contacting area between the metal strip and the current carrying roll. By this means, sparking at the contacting area is completely eliminated.

In a preferred embodiment shown in FIG. 4, a metal strip 1 to be heat treated is moved in the direction indicated by arrows at a constant speed, first between a current carrying roll 2a and a press roll 3a of elastic material, then around a guide roll 5 provided at the top and finally between a current carrying roll 2 and a press roll 3 made of elastic material. Auxiliary rolls 4 and 4a are associated with the respective roll sets 2, 3 and 2a, 3a which are immersed in tanks 6 and 6:; containing cooling water. Heating current is supplied to the metal strip 1 from a suitable A.C. source of supply 7 while the strip 1 is moved between current carrying rolls 2 and 2a which are driven by an electric motor 8. Current flowing through the strip 1 is effective to preheat it between rolls 2a and 5 and to elevate the temperature of the strip to the desired high value between rolls 5 and 2, the heated strip being quenched to finish heat treatment when it is introduced into the cooling water tank 6. As mentioned above, the press rolls 3 and 3a are urged with a substantial force against the current carrying rolls 2 and 2a to contact therewith' over curved areas. Thus, the contacts between the metal strip 1 and the current carrying rolls 2 and 2a are surface contacts which provide more positive contacts than the line contacts, thus decreasing contact resistance at the contacting areas. Moreover, as these rolls are positioned in water tanks, arcing between the rolls and the metal strip can be positively prevented.

Furthermore, asthe metal strip heated to an elevated temperature between rolls 5 and 2 is directly introduced into water without contacting any structure, whereby the risk of forming scratches on the surface of the strip metal,

which are easily formed by the prior heat treating apparatus because the strip is passed around guide rolls and the like while it is heated to an elevated temperature and, hence, is soft, is eliminated.

The purpose of auxiliary guide rolls 4 and 4ais to suitably guide the strip metal 1 so as to prevent damage to the strip due to electric sparks caused by undesired wavy contact between the strip and 'the current carrying rolls, it being understood that some of these auxiliary rolls can be dispensed with in certain applications.

The contact pressure exerted by the press rolls 3 and 3a can be suitably applied by water pressure means, oil pressure means, or electric motors. Oil pressure/pistoncylinder assemblies 9 and 9a may be provided to pull the rolls Sand 3a upwards to positions indicated by dotted lines to facilitate introduction of the metal strip through the sets of rolls. The applied pressure may be adjusted to provide appropriate contact areas depending upon the elasticity of the rolls 3 and 3a, the thickness of the metal strip and other factors. It will be obvious that the material, elasticity, heat resistance, hardness, etc. of the press rolls can be suitably selected in order to attain the objects of this invention.

By shaping the current carrying roll 2 so that it has a crowned peripheral surface, as shown in FIG. and by adjusting contact pressures on the right and left sides thereof, it is possible to move the metal strip positively along a path above the center of the roll without undue lateral displacement of the metal strip.

As shown in FIG. 6, the relative positions of the current carrying roll 2 and the press roll 3 and or the roll 2a and the roll 3a can be reversed. Again, the auxiliary guide rolls 4 and 4a made of rubber are provided to suitably guide the metal strip around the current carrying rolls 2 and 2a.

Although it is advantageous to maintain the temperatures of the water contained in the cooling water tanks 6 and 6a at a low value in order to prevent deterioration caused by the heat of the press rolls, said temperatures may be suitably varied dependent upon the material comprising these rolls. It is necessary to continuously circulate the water through the tanks 6 and 6a to provide adequate temperature control and it is advisable to use heated water exhausted from the cooling tank 6 for preheating the cooling tank 6a.

Referring again to FIG. 4, the upper guide roll 5 is supported at one end of a lever 10 which is pivoted on a fulcrum at 12 and is provided with a counterweight 11 on the opposite end. Vertical motion of this guide roll 5 is sensed by a suitable detector 13, the electrical output thereof being utilized to provide fine adjustment of relative rotating speeds between the current carrying rolls 2 and 2a, through an amplifier 14 and has a fine speed regulator 15. Thus, change in the heating temperature due to variation in the length of the metal strip travelling between the rolls 211-5 and 5-2 can be prevented while the tension of the metal strip is maintained constant.

In embodying the present invention, any other water solution or liquid except pure water may be used for cooling the parts to be cooled.

The general unique features of this invention may be enumerated as follows:

(1) As the metal strip to be heat treated is heated by electric current flowing through the strip itself, the temperature difference between the exterior surface and the interior portion of the metal strip is very small even when the heating time is substantially decreased by increasing the speed of feed. In other words, there is no risk of overheating the surface of the strip as in the case of heating the strip from the outside.

(2) As the press rolls made of an elastic material are pressed with substantial force against the current carrying rolls which are immersed in liquid, contacts between the strip and the rolls are made over surface areas, thereby greatly decreasing the contact resistance. As a result, abnormal local heating or sparking due to excessive contact resistance at the contacts can be prevented.

(3) Sparking is also prevented by the auxiliary rolls which are provided for the purpose of preventing sparking due to unstable contacts between the metal strip and the current carrying rolls at points immediately proceeding and succeeding the contact surfaces.

(4) Portions of the strip metal which is heated to a high temperature are directly introduced into a liquid for quenching without touching any other part of the apparatus, so that there is no risk of scoring or denting of the strip metal.

(5) The heat treating apparatus can always be operated in a stabilized condition because it does not comfew seconds, it can be operated intermittently without decreasing the efi'iciency of the furnace or without producing products of nonuniform quality.

(6) Where the dimensions and the material of the metal strips to be treated do not vary, the same heat treating condition can be easily and positively assured for all products by maintaining constant the applied voltage and speed of travel of the strip.

(7) Since press rolls made of an elastic material are used, overlapped joints between strips can easily pass between the press roll and the current carrying roll. By

making sufficiently large the contact area of these joints,

portions of the strip adjacent the joints can be heat treated equally as the remainder of the strip.

(8) By increasing the speed of travel of the strip, it is possible to decrease surface oxidation thereof to a substantially negligible order without using any special atmosphere.

(9) The temperature of the strip can be easily detected.

(10) If it is required to use any special atmosphere, it can be provided by the addition of simple equipment.

11) Under ordinary operating conditions, no auxiliary material or wasteful material is required; the only required utility supply being those of an electric power and a liquid.

(12) The heat treating apparatus of this invention requires power consumption of only 150 kWh/ton to anneal a strip of copper alloy which is far smaller than 300-500 kwh./ton required by the tunnel type resistance furnace commonly used for the same purpose. Thus, the efficiency is very high.

Examples Test material was a brass strip made of 67% Cu and 30% Zn and of 0.4x mm.

(13) The floor space of the heat treating apparatus of this invention is smaller than that of a conventional tunnel type furnace and the like which are commonly used.

(14) Introduction of the metal strip through the apparatus at the time of starting is very simple and easy.

(15) Even when electric power is interrupted and applied again after a certain time during the course of continuous heat treatment, it is possible to operate the apparatus so that the quality of the product remains uniform throughout the length of the strip. Stated in another way, it is possible to resume the operation of the apparatus without impairing the quality of the strip.

(16) While the heat treating apparatus of this inventioln has very high performance, its cost of manufacturing is ow.

Although only several preferred embodiments of the invention are shown in the drawings and described in the foregoing specification, it will be understood that the invention is not limited to the specific embodiments de scribed, but is adaptable to modification and rearrangement and substitution of parts and elements without departing from the spirit and scope of the invention.

I claim:

1. A continuous heat treating apparatus for metal strips comprising: a first set of rolls; a second set of rolls spaced apart from said first set, guide roll means between each set, each of said first and second sets including a current carrying roll with a conductive strip-engaging surface, a resilient concave pressure shoe of a size corresponding about to the size of current carrying roll, means to apply an AC. current across said strip-engaging surface so as to pass a heating current through said metal strip, means to drive said current carrying rolls, means to urge said shoes against said current carrying rolls to cause extended surface contact over a large arc therebetween, and a cooling liquid tank to immerse said current carrying roll and said shoe, means to move a metal strip to be heat treated between the shoe and the current carrying roll of said first set, around said guide roll means, and between the shoe and current carrying roll of said second set, and means to pass current through said metal strip via said current carrying rolls, while it is moving between said current carrying rolls.

2. The continuous heat treating apparatus according to claim 1,.wherein a guide roll of said guide roll means is positioned above and at an intermediate point in the work flow path between said first and second sets of rolls.

3. The continuous heat treating apparatus according to claim 2, wherein a pair of auxiliary guide rolls are provided adjacent each said surface contact area so as to maintain said metal strip away from said current carrying roll.

4. The continuous heat treating apparatus according to claim 3, where said current carrying roll is disposed horizontally and said shoe is pressed against the upper surface thereof by means of a piston-cylinder device.

so as to heat treat said metal strip 6 5. The continuous heat treating apparatus according to claim 4, wherein said guide roll means is counterbalanced by means of a weight so as to apply tension to said metal strip.

6. The continuous heat treating apparatus according to claim 5, wherein a detector is provided to operate cooperatively with said guide roll means to detect displacemennts thereof, and wherein means responsive to the output of said detector is provided to regulate the travelling speed of said metal strip and to maintain constant the tension of said metal strip.

7. The continuous heat treating apparatus according to claim 1, wherein said current carrying roll is a roll having a crowned surface in the direction parallel to its arms.

References Cited by the Examiner UNITED STATES PATENTS RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, Examiner. B. STEIN, Assistant Examiner. 

1. A CONTINUOUS HEAT TREATING APPARATUS FOR METAL STRIPS COMPRISING: A FIRST SET OF ROLLS; A SECOND SET OF ROLLS SPACED APART FROM SAID FIRST SET, GUIDE ROLL MEANS BETWEEN EACH SET, EACH OF SAID FIRST AND SECOND SETS INCLUDING A CURRENT CARRYING ROLL WITH A CONDUCTIVE STRIP-ENGAGING SURFACE, A RESILIENT CONCAVE PRESSURE SHOE OF A SIZE CORRESPONDING ABOUT TO THE SIZE OF CURRENT CARRYING ROLL, MEANS TO APPLY AN A.C. CURRENT ACROSS SAID STRIP-ENGAGING SURFACE SO AS TO PASS A HEATING CURRENT THROUGH SAID METAL STRIP, MEANS TO DRIVE SAID CURRENT CARRYING ROLLS, MEANS TO URGE SAID SHOES AGAINST SAID CURRENT CARRYING ROLLS TO CAUSE EXTENDED SURFACE CONTACT OVER A LARGE ARC THEREBETWEEN, AND A COOLING LIQUID TANK TO IMMERSE SAID CURRENT CARRYING ROLL AND SAID SHOE, MEANS TO MOVE A METAL STRIP TO BE HEAT TREATED BETWEEN THE SHOE AND THE CURRENT CARRYING ROLL OF SAID FIRST SET, AROUND SAID GUIDE ROLL MEANS, AND BETWEEN THE SHOE AND CURRENT CARRYING ROLL OF SAID SECOND SET, AND MEANS TO PASS CURRENT THROUGH SAID METAL STRIP VIA SAID CURRENT CARRYING ROLLS, SO AS TO HEAT TREAT SAID METAL STRIP WHILE IT IS MOVING BETWEEN SAID CURRENT CARRYING ROLLS. 